LW mp3 Sound Quality?

[Rhohl]

Regarding sound quality of the MP3's I've downloaded from LW...

Wondering why(?) the playback of music files (generally)
have too much volume on the instrumental part, with vocals which are too weak?
And, the bass is too heavy(strong)?

Seems to happen regardless of bit rate and the equalizer settings of my chosen player (iTunes 2)
can improve, only marginally, the quality (or balance) of the sound.

Is it the player? Should I use something else?(for a Mac)
Or, is it the nature of the MP3 format?
The sound reminds me of the early days of cassettes (& 8-tracks)
when the bass was often boosted to compensate
for the relatively poor portable sound systems (and bass speakers) available.

My speakers are fairly good...and my own (installed from my CD's @128bits)) music, sound OK.

Any ideas?